The event marker of the present invention is useful in connection with radar homing and warning systems. An aircraft may be illuminated by a series of radar RF bursts or impulses during particular sub-intervals or time slots within a series of pulse repetition intervals, and the production of what is known as an event marking output pulse during one time slot within each pulse repetition interval (PRI), is employed to generate a jamming signal to produce a retransmitted burst of RF energy, which will coincide with the predicted reception of the next incoming radar signal. Since the incoming impulses will often not be received within the same time slot during each PRI, it is often necessary for the computer to calculate changes in the predicted reception time of the next RF burst. In other words, the future event to be indicated or marked occupies a different time slot within each PRI since the phase and/or frequency of the series of impulses will be changing in a predictable manner. By measuring these changes, the computer is able to predict the occurence of the next RF burst or future event. This computer operation is well known by those in the radar homing and warning community, and the manner in which the computer operates is beyond the scope of this invention.
In accordance with the prior art, a random access memory (RAM) having a large number of cells or storage elements corresponding to the required number of subintervals examined for the occurrence of the event during each pulse repetition interval, is provided. A binary 1is inserted only into one of the cells. A memory access control circuit controlled by a binary address number produced by a binary counter sequentially scans all cells once during each pulse repetition interval, in order to detect the presence of a single binary 1 which indicates the occurrence in the event in time. Upon the detection of the binary 1, a "data out" lead of the RAM is marked to establish the occurrence of the event during the pulse repetition interval. At this time the just-addressed cell containing the binary 1 is cleared, and a binary 1 is either rewritten in such cell or written into another cell if a computer determines that the occurrence of the event in time is to changed. For example, a single RAM has been employed having 65,536 (2.sup.16) cells, all of which are scanned once during one pulse repetition interval. The binary counter counts up to 2.sup.16 to effect each scan of the RAM. It is highly desirable to drastically reduce the number of storage elements of this RAM and yet fully maintain the above-mentioned function.